Field of the Invention
The embodiments of the present invention relate generally to bio-based superabsorbent polymer materials based on renewable, natural polymers. More specifically, the embodiments disclosed herein relate to a cross-linked superabsorbent polymer material derived from natural polymers that includes proteinaceous substrates and having superabsorbent properties in aqueous fluids, and a method to produce such a crosslinked superabsorbent polymer material.
Discussion of the Related Art
A superabsorbent polymer is a crosslinked polymer network that is capable of absorbing and retaining an extraordinary amount of water (10˜1000 times its own weight). The thermodynamic mechanism of a superabsorbent polymer requires the polymer network to have sufficient numbers of hydrophilic, especially ionic groups. The hydrophilicity of these groups drives the superabsorbent polymer to absorb and retain large amounts of water or aqueous fluids. Crosslinking is necessary to prevent the polymer from dissolving in water and allow structural integrity of the superabsorbent material. The ionic content and crosslinking degree of the polymer network determine the properties of the superabsorbent material such as degree of swelling of the superabsorbent hydrogel, mechanical strength and water retention capacity.
Conventional superabsorbent polymer by volume of production according to the state of the art is polyacrylic acid-based, which often includes sodium salts of polyacrylic acid and a copolymer of acrylamide and acrylic acid. Polyacrylic acid itself is synthesized through free radical polymerization of acrylic acid, a monomer predominately derived from oxidation of propylene. Crosslinking of polyacrylic acid-based polymers is usually provided by a chemical compound called crosslinking agent that contains at least two unsaturated carbon-carbon double bonds. Superabsorbent polymers are used for applications such as baby diapers and adult hygiene products, soil additives, water purification, oil treatment, and industrial dewatering. Growing demand of superabsorbent polymer materials and increasing oil price strongly motivates the utilization of bio-based alternatives to current superabsorbent materials.
Background information on a protein-based natural polymer to make superabsorbent polymers is described and claimed in U.S. Pat. No. 8,148,501, entitled, “ABSORBENT PROTEIN MEAL BASE HYDROGELS,” issued Apr. 3, 2012, to Benecke et al., including the following, “absorbent hydrogels are formed by reacting a protein meal base, a radical initiator and a polymerizable monomer. Optionally, a cross-linking agent and/or a radical accelerant, such as tetramethylethylenediamine (TMEDA) or sodium bisulfite (NaHSO3), is also added to the mixture. Preferably, the radical initiator is ammonium persulfate (APS) or potassium persulfate (KPS), and the cross-linking agent is preferably trifunctional trimethylolpropane trimethacrylate (TMPTMA) or methylene bisacrylamide (MBA). The polymerizable monomer is preferably acrylic acid, or a combination of acrylic acid and acrylamide.”
Background information on a superabsorbent biodegradable hydrogel based on acylated-protein but substantially free of residual cross-linkers is described and claimed in U.S. Pat. No. 6,310,105, entitled, “CARBOXYL-MODIFIED SUPERABSORBENT PROTEIN HYDROGEL,” issued Oct. 30, 2001, to Damadoran, including the following, “the present invention is a biodegradable, reversibly-swellable, polyvalent cation-binding, protein hydrogel which comprises an acylated protein matrix in which the acylated protein matrix is crosslinked with a bifunctional crosslinking reagent, and treated with a polar organic solvent, and a method of making the same.”
Background information on a manufacturing methodology of a superabsorbent polymer based on modified polysacharides is described in U. S. Application No. 2013/0338354, entitled, “RENEWABLE SUPERABSORBENTS,” published Dec. 19, 2013, to Albertsson et al., including the following, “ . . . the present invention relates to a crosslinked polymer material derived from hydrolysates comprising hemicelluloses and having superabsorbent properties in water based fluids, and a method to produce such a crosslinked polymer material.”
The above cited art, while respectively beneficial, nonetheless have drawbacks that are addressed by the teachings herein. For example, the renewable content in the above cited art is usually low when beneficial high water absorbency is achieved. It is also to be noted that the mechanical strength of the hydrogel is often compromised due to the way the natural polymer and synthetic component of the desired superabsorbent hydrogel is assembled. In addition, chemical modifications of polysaccharides, such as in U. S. Application No. 2013/0338354, involve expensive chemicals and/or processes. Moreover, while the method based on the modified polysaccharides through hydroxyl groups lends itself to a superabsorbent material, the reactivity of the hydroxyl groups contained in the polysaccharides is less than desirable.
Accordingly, there is a need in the art for an improved method of manufacturing bio-based superabsorbent polymer materials through an approach of macromonomer derived from natural proteinaceous polymer(s). The embodiments disclosed herein address such a need.